DE 10 2007 032 949 (and related US 2010/0226793) discloses an electronic brake pressure control assembly with analog controllable solenoid valves (what are known as pulse-width modulated (PWM) valves). According to the design of solenoid valves, an electric valve current flows through an electric magnet coil for opening and closing the valve, which magnet coil magnetically actuates what is known as the valve plunger which controls the hydraulic fluid volumetric flow. Such valves are used as inlet valves or isolating valves within a motor vehicle wheel brake pressure control system. For an active pressure build-up (independent pressure build-up without brake actuation by the driver), the brake pressure control assembly comprises a pressure build-up assembly (pump) which is driven by an electric motor. The mechanical construction of the pump assembly may be in the form of a reciprocating piston pump. This type of pump can comprise two or more pistons. Especially where small adjustments of wheel brake hydraulic actuation pressures are desired, it has been shown that fluctuations in the delivered pressure volume at the outlet of the pump can occur, especially in the case of pumps with a few number of pistons, which fluctuations make sufficiently accurate pressure setting by the electronic valve control means difficult. This is especially disruptive in the case of distance control systems such as for ACC (adaptive cruise control) systems, since even comparatively small pressure fluctuations can be sensed by the driver.
The present invention is based on the object of specifying an electronic control device which comprises a method, by way of which the volumetric flow which is generated by the pump assembly can be smoothed and in the process the reliability of other control functions which do not require a volumetric flow which is smoothed to this extent is not impaired.
According to the invention, this object is achieved by the electronic control device described and claimed herein.
The electronic control device according to the present invention includes a control device which carries out a pressure control operation in motor vehicle braking systems and by way of which solenoid valves which can be driven and controlled by electric current via an actuating electronic system are actuated for pressure control. The solenoid valves are used for at least one wheel brake circuit isolating valve, at least one wheel brake pressure inlet valve, and at least one wheel brake pressure outlet valve. A pump assembly which generates a very accurately metered volumetric flow with a periodically fluctuating amplitude at the outlet of the assembly is actuated (active pressure build-up) as a function of a pressure request, as is the case, for example, in a distance control (ACC) operation. Corresponding control operations are called control operations which perform an intervention for driving stability control which is not critical to safety. Here, the wheel brake circuit isolating valve provides a pressure limiting function for the associated wheel brake circuit in such a way that excess volume of brake fluid in the brake circuit is discharged in a metered manner into a connected reservoir volume by the valve which is in the control mode. The pressure in the brake circuit is therefore determined by the pump performance in conjunction with the quantity of the volume outflow at the isolating valve.
According to the invention, firstly the electric coil current for the actuation of the isolating valve is modulated periodically, the cycle of the modulation corresponding to a major cycle of the volumetric or pressure fluctuation which is caused by the pump assembly. The fluctuations in the delivery volume which are generated by the pump assembly can be greatly reduced or even suppressed virtually completely by this measure, without there having to be mechanical means, such as cascade baffles, connected with the pump outlet. Secondly, monitoring is carried out as to whether a control operation which represents an intervention for driving stabilization which is critical to safety has to be carried out, such as skid control, antilock brake system (ABS), or road handling control (ESP, ESC). If this is the case, the solenoid valve which is used for smoothing the pump flow is at least temporarily no longer actuated periodically. The list of the above control operations critical to safety preferably also comprises further control functions which primarily have an influence on the driving stability.
A determination of the cycle of the isolating valve modulation is preferably brought about by a position detection means which is arranged on the pump assembly or on an associated electric motor. According to a first preferred embodiment, the position detection means is preferably a displacement or angle sensor which is connected to a movable part of the pump assembly. Suitable modulation of the isolating valve current is preferably carried out with a curve in accordance with the position of the eccentric component or the piston of the pump assembly, or the phase position (angular position) of a motor armature which is driving the pump, the shape of which curve has to be selected suitably as a function of the desired correction quality and the options in terms of switching technology. Here, the progression of the curve and its influence on the elimination of the volumetric flow fluctuations can readily be determined experimentally. It is expedient that the theoretically optimum progression of the curve is simplified in order to implement it electrically in a relatively simple manner. The curve for the current modulation is therefore preferably a rectangular, triangular, or sine curve. The angular position of the pump assembly or the motor which actuates the assembly can be produced, for example, according to the method which is described in DE 10 2008 018 818.
According to a further preferred embodiment for a position detection means, it is a device which determines the rotor position of a brushlessly actuated electric motor. In the case of a brushlessly actuated electric motor with a position sensor, the sensor signal or the electronics for the motor, for example, can be used to detect the rotor position. In the case of a brushless electric motor without position sensors, the rotor position of the electric motor can be obtained, for example, from the signals of the motor actuation electronics.
According to one embodiment which is likewise preferred as an alternative to the position detection means, the cycle for the pressure modulation is not derived by way of a position detection means on the pump assembly or its driving motor, but rather from the actuating electronic system for the isolating valve current, that is to say directly via the pressure profile or by evaluation of another pressure-dependent signal (for example, from a pressure sensor). The magnetic flux in the region of the actuating magnetic field of the fluid valve which is used for monitoring the fluctuations allows conclusions to be made about the pump fluctuations, since they act via the fluid connecting lines on the plunger of the valve. The flux change which is caused is preferably determined via the induction signal by means of a current loop in the magnetic circuit of the fluid valve. The fluid valve which is used for determining the pressure is connected hydraulically, in particular, to the outlet side of the pump. The evaluation of the induction signal allows a conclusion to be made about the cycle of the pressure fluctuations, since the cycle of the induction signal is substantially consistent with the cycle of the pressure fluctuations.
In addition to the above-described measures, the pump assembly performance can expediently be set or adjusted by way of a controller in a manner which is additionally suitable for optimizing the control operation. To this end, the motor current is particularly preferably modulated in a suitable way while the motor is revolving, as is described in DE 10 2008 018 818.
As has already been described further above, the magnetic field, more precisely the magnetic flux, changes in the region of the valve coil in the case of a plunger movement which is caused by a periodic or else non-periodic pressure change at the solenoid valve which is used for measuring the pressure (differential pressure change). According to a first preferred embodiment, this change can be determined by way of a current loop in the region of the coil magnetic field or directly via the actuating coil. In what is known as the TPM (for “Tappet Position Monitoring”) method, the position of the valve plunger or the plunger force is preferably set by the actuating electronic system by means of a control operation to a defined setpoint value. Here, in particular, an induction signal of the current loop which is recorded in the region of the valve coil is used as an actual value. An evaluation of the plunger reaction in a particularly sensitive manner is possible when the plunger is in or close to a force equilibrium between magnetic force (minus or plus the spring force) and hydraulic force. If the forces lie far apart from one another, the plunger cannot react, or cannot react sufficiently sensitively, to a pressure change. It can then be the case that the plunger reacts to only a minimum extent to a pressure change on the valve, without the plunger position changing perceptibly. According to one preferred embodiment, however, the TPM control electronic system can adjust the valve flow to such an extent that the predefined plunger position is not changed. In this case, only the force conditions at the valve change (a greater valve flow is set on account of a higher pressure difference). In this case, the pressure pulses can be determined only by way of the actuating variable which is processed in the control operation or by way of the actual value changes. According to a further preferred embodiment, the flux change is therefore determined via changes in the actuating variables or the actual variables within the TPM control operation.
Moreover, the invention relates to the use of the above-described control device in conjunction with distance control operations (ACC). The control device comprises further control functions, such as at least an antilock brake system (ABS) and electronic stability program (ESP) or possibly further control operations, such as a traction control system (ASR, TCS), etc.